The U.S. Court of Appeals ruled yesterday that the D.C. Police Department should not have dismissed a probationary officer in 1972 for publicly advocating a "blue-flu" job action during a police pay dispute.

The Appeals Court reversed a 1978, decision by U.S. District Judge Louis F. Oberdorfer who had ruled that the officer brought his trustworthiness into question by indicating that he would participate in a "blue-flu," a substitute for a strike in which police officers falsely report that they are too ill to work.

The case had been brought on behalf of James R. Tygrett by attorneys for the American Civil Liberties Union. Tygrett, who works as an administrator for a charter airline in Ohio, could now seek to be reinstated by the police force. He had not sought money damages.

The lower court said that Tygrett's apparent willingness to falsely report he was sick "seriously impaired" his ability to do his job -- principally his credibility as a witness in court. Therefore, Oberdorfer had said, the department's dismissal was justified.

Judge Abner J. Mikva, writing for the appeals court yesterday, said, however, that the department had not raised the question of Tygrett's truthfulness and his effectiveness as a police officer when it notified him that he was dismissed from the force.

Rather, Mikva said, the department concentrated on Tygrett's apparent intent to violate an antistrike ordinance on possible damage to the department's image and its efforts to carry out its obligations to the community.

"As the record affirms throughout, Tygrett was discharged because advocated strike actions, not because he lied," Mikva wrote. He was joined in his decision by Judge Edward A. Tamm and Senior Judge Edward J. Lumbard of the 2nd Circuit Court of Appeals, sitting on special assignment.

The job of the courts is to balance the employe's free speech rights and the government's interest in promoting the efficiency of the services it performs for the public, Mikva wrote. Based on standards set down by the Supreme Court, Tygrett's dismissal would be valid if the department showed that its work was impaired by his conduct or if his statements had hurt his effectiveness as a police officer, Mikva said.

Mikva pointed out that shortly before he was dismissed, Tygrett was recommened for a permanent appointment to the police force. Later, the department wrote a letter of recommendation for Tygrett and made no mention of his reputation for truthfulness, Mikva said.

In effect, the department constructed a legal reason for Tygrett's firing after the fact, Mikva said. He said the court cannot "rummage throughout the record of a case" and try to come up with a rationable to support a dismissal, especially in cases such as Tygrett's where the law required the District to provide written reasons for its decision.

The District government could now ask the full appeals court to hear the case or seek review by the Supreme Court.